The detection of chloride ions is critical for a number of different applications, including but not limited to, health and industrial applications. Numerous indicating devices for the detection of chloride ions are known in the art. The majority of known indicating devices for chloride ions employ a silver chromate or silver dichromate hexavalent chromium (Cr(VI)) compound as the indicating agent, which contains chromium in an oxidation state of +6. Exposure to hexavalent chromium over a prolonged period of time, however, is known to pose significant health risks.
For example, if hexavalent chromium comes into contact with the eyes and skin, hexavalent chromium may cause irritation and even permanent damage if the exposure is long enough. In addition, if hexavalent chromium comes into contact with a cut or laceration on the skin, the compound may cause chrome ulcers, which typically take a long time to heal and may leave a visible scar. If inhaled, hexavalent chromium may irritate the nasal passages, throat, and lungs. Further, prolonged exposure to hexavalent chromium may result in damage to the mucous membranes, nosebleeds, perforation of the septum, and an increased risk of developing lung cancer. Moreover, when exposed to vitamin C in vivo, hexavalent chromium may result in severe damage to the individual's DNA inside the lung's cells. Even further, the International Agency for Research on Cancer (IARC) lists hexavalent chromium as a known human carcinogen.
The Occupational Safety and Health Administration (OSHA) has set acceptable exposure levels for hexavalent chromium in a variety of occupations as follows: 0.005 mg/m3 or 5 micrograms/m3 TWA for General Industry; 0.005 mg/m3 or 5 micrograms/m3 TWA for the Construction Industry; and also 0.005 mg/m3 or 5 micrograms/m3 TWA for the Maritime Industry. Further, the National Institute for Occupational Safety and Health (NIOSH) has deemed 0.001 mg Cr(VI)/m3 10-hr TWA to be the recommended exposure limit.
In addition to the above concerns, hexavalent chromium-containing devices must also be handled carefully after use and disposed of properly. Hexavalent chromium is prevalent on many environmental lists such as the Resource Conservation and Recovery Act (RCRA) in the United States, the Pollution Release and Transfer Register (PRTR) in Japan, and the European Union Hazardous Waste Directive, for example. While devices and methods that reduce exposure levels of hexavalent chromium may be used, completely eliminating the use of hexavalent chromium in the detection of chloride ions would be more desirable. To date, the known prior art has failed to provide workable, low cost, and readily visible chromium-free indicators and methods for the detection of chloride ions.